In internal combustion engines, e.g., gasoline or Diesel piston engines, to increase the performance, the air charge in a combustion chamber of the internal combustion engine is increased by the use of a compressor, such as an exhaust gas turbocharger. The pressure with which the air is pressed into the combustion chamber of the internal combustion engine is also designated as boost pressure, and is generally measured in the vicinity of the combustion chamber by a pressure sensor. The pressure signal is supplied to a closed control loop which controls the exhaust gas turbocharger and thereby sets a desired boost pressure.
Exhaust-gas turbochargers have a characteristic time constant, and thus they react comparatively sluggishly to changed control signals, which makes the regulation of the boost pressure more difficult. Therefore, it is advantageous if a direct state variable of the exhaust gas turbocharger that is to be regulated is recorded, e.g., the rotary speed of the compressor of the turbocharger, which is particularly suitable for this purpose.
It is an object of the present invention to provide a method which makes possible a cost-effective and reliable recording of the rotary speed of a compressor.